class Hello extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      opacity: 1.0
    };
  }
  componentDidMount() {
    this.timer = setInterval(
      function() {
        var opacity = this.state.opacity;
        opacity -= 0.05;
        if (opacity < 0.1) {
          opacity = 1.0;
        }
        this.setState({
          opacity: opacity
        });
      }.bind(this),
      100
    );
  }

  render() {
    return (
      <div style={{ opacity: this.state.opacity,fontSize:'25px' }}>Hello {this.props.name}</div>
    );
  }
}

ReactDOM.render(<Hello name="world" />, document.getElementById("root"));
